Technical Field
The present invention relates to the supply of electrical power to an elevator system in general, and to devices capable of storing electrical power for an elevator in particular.
Background Information
In some applications, according to the local energy market and grid power quality, it is desirable to equip a grid-powered elevator with an energy accumulation device that can be accessed during peak power demand periods or periods when grid power is not available (i.e., blackout mode).
This accumulation device can be also used, to regeneratively recover energy when the elevator is operating in a braking phase in order to achieve a better performance in terms of energy efficiency, and also greater duration when operating in blackout mode.
Lead acid batteries are sometimes used as a reserve power source in elevators due to the relative low cost of a battery pack that can cover the energy demand of the entire elevator system for more than one day.
Unfortunately, lead acid batteries typically have a relatively short service life, and are inefficient at regeneratively recovering high power peaks that are available when an elevator is operating in a braking phase. These two factors make it difficult to take advantage of power regenerated by an elevator system.
Using other kinds of chemical batteries (e.g., ion lithium, nickel cadmium, etc.), could improve battery life and efficiency. These types of batteries can however, be prohibitively expensive when configured to cover significant periods of blackout mode operation in a low rise residential application. In addition, in many countries there are compulsory safety measures related to implementation of high energy density batteries for transportation and storage.
Unfortunately, the current battery market does not offer a single device that can store sufficient energy to cover all the requirements discussed above, at a price that is competitive in the low rise residential market.
What is needed is an elevator system with a drive system with the capability to cover peak power demands of an elevator running with very low power demand from a grid, with excellent regenerative features (like grid regenerative drive efficiency), which system can be used during grid power outages (e.g., blackouts lasting from a few seconds to more than one day) to cover, for example, specific customer needs in terms of outage duration based on local power grid quality, and which system has the reliability of an elevator normally operating under full grid power.